Typically, highway bridges are constructed of discrete concrete slabs supported on pillars and disposed end to end with an expansion gap between adjacent slabs. A continuous hot rolled asphalt roadway or concrete roadway is formed over the slabs to provide the bridge deck surface.
A common problem at bridge joint regions is cracking and deterioration of the asphalt and deck members. This deterioration is attributed to (1) expansion, contraction, or other movement of deck members which disrupts the asphalt layer above the expansion gap between slabs and (2) vehicular impact on the asphalt roadway immediately above the expansion gap. As weather conditions change, the concrete slabs contract or expand causing movement of the slabs in the gap region. The continuous asphalt roadway across the bridge surface and overlying the expansion gaps is pulled apart or crunched together in the region of the gaps due to the supporting deck movement. Cracks and potholes result in the asphalt. This is hazardous to drivers and also permits water and asphalt debris to penetrate the bridge construction where they can lead to deterioration of the supporting bridge structure.
A similar problem results from vehicular impact on the asphalt immediately above the gap or joint. If the asphalt is not properly supported from below at the gap region, impact stresses push the asphalt down into the gap area where it can break off the upper corners of the deck members. Water seeping into the structure will also expand or contract causing further cracking in the structure, and the debris from deterioration may fall into the gap blocking necessary free movement of the deck members.
An early solution attempted for this problem was to provide for a stronger support in the asphalt immediately above the joint. This was accomplished by cutting a channel in the asphalt surface about 30 cm wide at the location of the joint. Two strips of epoxy mortar were applied to the deck members on either side of the expansion gap and a continuous strip of plastic or rubbery sealing material wa applied immediately above the gap. The hardness of the material above the gap was intended to provide support so that vehicular impact stress would not cause deterioration. The hardness of the center rubber did prevent the asphalt from cracking directly above the gap. However, this hardness proved to be a disadvantage because it caused the softer surface on either side of the relatively harder strip to break up. Debris from cracking was not accommodated by the hard strip and this also exerted damaging pressure to surrounding areas.
More recently, attempts have been made to overcome these disadvantages. A method for sealing bridge deck joints by filling a channel cut around and above the gap with a flexible composition of chips of stone aggregate in a rubberized bitumen matrix is proposed in U.S. Pat. No. 4,324,504 to Cottingham. The rubberized bitumen matrix was composed of bitumen, tire crumb rubber, fine sand, and limestone powder. The rubberized binder was intended to bind the stone aggregate together so that the joint would have sufficient flexibility to withstand movement of the concrete slabs without the surface cracking. However, the solid support needed to withstand impact over the gap is not provided by the Cottingham joint. Vehicular impact stress causes the aggregate to move or jolt suddenly within the matrix, eventually breaking the bond with the rubberized matrix and ultimate deterioration of the joint.